Measured and modelled effect of land use change from temperate grassland to Miscanthus on soil carbon stocks after 12 years

Authors Organisations
Type Article
Original languageEnglish
Pages (from-to)1173-1186
Number of pages14
JournalGCB Bioenergy
Volume11
Issue number10
Early online date21 May 2019
DOI
Publication statusPublished - 01 Oct 2019
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Abstract

Soil organic carbon (SOC) is an important carbon pool susceptible to land use change. There are concerns that converting grasslands to the C4 bioenergy crop Miscanthus (to meet demands for renewable energy) could negatively impact SOC, resulting in reductions of greenhouse gas mitigation benefits gained from using Miscanthus as a fuel. This work addresses these concerns by sampling soils (0‐30 cm) from a site twelve years (T12) after conversion from marginal agricultural grassland to M. x giganteus and four other novel Miscanthus hybrids. Soil samples were analysed for changes in below ground biomass, SOC, and Miscanthus contribution to SOC (using a 13C natural abundance approach). Findings are compared to ECOSSE soil carbon model results (run for a land use change from grassland to Miscanthus scenario and continued grassland counterfactual), and wider implications are considered in the context of life cycle assessments based on the heating value of the dry matter (DM) feedstock.

Mean T12 SOC stock at the site was 8 (+/‐ 1, standard error) Mg C ha−1 lower than baseline time zero stocks (T0), with assessment of the five individual hybrids showing that whilst all had lower SOC stock than at T0 the difference was only significant for a single hybrid. Over the longer term, new Miscanthus C4 carbon replaces pre‐existing C3 carbon, though not at a high enough rate to completely offset losses by the end of year 12. At the end of simulated crop lifetime (fifteen years) the difference in SOC stocks between the two scenarios was 4 Mg C ha−1 (5 g CO2‐eq MJ−1). Including modelled land use change induced SOC loss, along with carbon costs relating to soil nitrous oxide emissions, doubled the greenhouse gas intensity of Miscanthus to give a total global warming potential of 10 g CO2‐eq MJ−1 (180 kg CO2‐eq Mg−1 DM).

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Keywords

  • land use change, bioenergy, miscanthus, pasture, soil organic carbon, life cycle assessment